Dynamic leak detection system in propane heat exchangers

ABSTRACT

Systems and processes for detecting leaks into a refrigeration system having a heat exchanger where the process side is configured to operate at a higher pressure than the refrigerant side. The system includes a refrigerant circulation system including a refrigerant feed pipe fluidly connected to and configured to provide a refrigerant to an inlet of the refrigerant side of the heat exchanger, as well as a refrigerant effluent pipe fluidly connected to and configured to receive a refrigerant from an outlet of the refrigerant side of the heat exchanger. One or more sensors are provided, the sensors being configured to measure a property of the refrigerant, such as temperature, pressure, or flow rate, for example. Additionally, the system for detecting leaks includes a digital control system configured to provide an alert when a signal from at least one of the one or more sensors is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.

BACKGROUND

Plants processing natural gas liquids (NGL) or other light hydrocarbon gases often receive feeds that are sour, containing hydrogen sulfide, carbon dioxide, other acid gases, and possibly water. Systems processing such gases include unit operations, including heat exchangers, which present an opportunity for introduction of the acid gases into a refrigerant, and thus the opportunity for corrosion within the refrigerant system. Small leaks are relatively hard to detect, but can cause severe problems within a refrigerant system if not timely addressed. Accordingly, there exists a need for mechanisms to detect leakage of sour natural gas and contamination of the refrigerant to prevent the undesirable corrosion.

Various systems have been proposed to detect the leakage of sour gas into the refrigerant, including various online composition analyzers, used to sample and measure a composition of the refrigerant in various streams to detect the presence of acidic components in the refrigerant. However, these efforts are capital intensive and require preventative maintenance efforts.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, embodiments disclosed herein relate to a natural gas processing facility. The natural gas processing facility may include a feed line providing a mixture of acid gases and hydrocarbons, such as a mixture of methane, ethane, propane, and optionally butane and other heavier hydrocarbons. The natural gas processing facility may also include a compression section, including one or more compressors configured to receive the mixture from the feed line, increase a pressure of the mixture and output a compressed mixture of the hydrocarbons and acid gases. A flow line may provide the compressed mixture to a stripper configured to separate the compressed mixture into an overhead product including the acid gases, methane, ethane, and at least a portion of the propane and a bottoms product including propane as well as any butane and other heavier hydrocarbons.

The natural gas facility also includes a propane chiller, a deethanizer, and an overhead condenser. The propane chiller is configured to receive the overhead product from the stripper, chill the overhead product, and output a chilled overhead product via a flow line to the deethanizer. The deethanizer is configured to separate the chilled overhead product into an overhead fraction including the acid gases, methane and ethane, and a bottoms product comprising propane and any butane and other heavier hydrocarbons. The overhead condenser is configured to condense at least a portion of the overhead fraction, provide reflux to the deethanizer, and to output an overhead vapor product including methane, ethane, and acid gases.

The natural gas facility further includes a closed loop refrigeration system configured to provide a refrigerant to each of the propane chiller and the overhead condenser. One or more sensors are included to measure a property of the refrigerant, wherein the one or more sensors are disposed along a refrigerant feed line providing a refrigerant flow to the propane chiller or to the overhead condenser, along a refrigerant effluent flow line from the propane chiller or the overhead condenser, or both.

The natural gas facility further includes a digital control system configured to receive a signal from each of the one or more sensors and to provide an alert when a signal from one of the one or more sensors is indicative of a leak of acid gases into the closed loop refrigeration system.

In another aspect, embodiments herein are directed toward a system for detecting leaks into a refrigeration system. The system may include a heat exchanger having a process side and a refrigerant side, wherein the process side is configured to operate at a higher pressure than the refrigerant side. The system also includes a refrigerant circulation system including a refrigerant feed pipe fluidly connected to and configured to provide a refrigerant to an inlet of the refrigerant side of the heat exchanger, as well as a refrigerant effluent pipe fluidly connected to and configured to receive a refrigerant from an outlet of the refrigerant side of the heat exchanger. One or more sensors are provided, the sensors being configured to measure a property of the refrigerant, such as temperature, pressure, or flow rate, for example. Additionally, the system for detecting leaks includes a digital control system configured to provide an alert when a signal from at least one of the one or more sensors is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.

In yet another aspect, embodiments herein are directed toward a process for processing natural gas liquids. The process may include chilling a feed comprising acid gases, methane, ethane, and propane via indirect heat exchange with a refrigerant in a heat exchanger, wherein the feed is at a higher pressure than the refrigerant. A temperature, pressure and/or flow rate of refrigerant feed and effluent to and from the heat exchanger, respectively are measured via one or more sensors. The process also includes detecting a leak, automatically via a digital control system, based on a change or a relative change in a measured temperature, pressure, or flow rate of refrigerant in the refrigerant loop upstream and/or downstream of the heat exchanger. In some embodiments, the process may further include isolating, automatically via the digital control system, the heat exchanger having the leak.

Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a typical shell and tube heat exchanger.

FIG. 2 is a simplified process flow diagram of a natural gas processing facility according to embodiments herein.

FIG. 3 is a simplified process flow diagram of the deethanizer and associated equipment of the natural gas processing facility.

FIG. 4 is a simplified process flow diagram of the refrigeration system associated with the deethanizer feed chilling and overhead condensation systems.

FIG. 5 is a simplified diagram of a control system that may be useful in embodiments herein.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to dynamic leak detection in refrigeration systems. More specific embodiments herein relate to dynamic leak detection in propane refrigerant systems. Even more specific embodiments herein relate to dynamic leak detection and remediation in propane refrigerant systems in a natural gas processing facility. The leak detection may be provided by temperature, pressure and/or flow sensors and associated measurements of appropriate flow streams, where such may provide for a rapid determination of a leak event while avoiding the need for the more expensive and operationally difficult compositional sampling and measurement systems.

Referring now to FIG. 1 , a typical shell and tube heat exchanger 8 is illustrated, which includes two inlets (tube side inlet 10 and shell side inlet 26) and two outlets (tube side outlet 22 and shell side outlet 28). Tube side flow is directed from inlet 10 into inlet or front-end header 12, through an interior of the tubes 16, consolidated in outlet or rear-end header 20, and then recovered via outlet 22. Shell side flow is directed into the shell 24 of the exchanger via shell inlet 26, the flow passing over an exterior of the tubes 16 and around baffles 21 and recovered via shell outlet 28. The tubes 16 are typically welded to tubesheets 14 and 18 segregating the shell side flow from the tube side flow.

Other various forms of heat exchangers may be used, including exchangers having single or multiple passes on the shell side, as may be provided by baffles, and/or single or multiple passes on the tube side, as may be provided by baffles in the inlet and outlet header, U-shaped tubes, or other various configurations as known in the art. Exchangers may also have multiple inlets or outlets, such as vapor and liquid outlets, for example.

While corrosive compounds may attack the metal at any point within the exchanger, it is common for failures to occur at the weld connecting the tubes to the tube sheet. The tube sheet itself may also fail, as may individual tubes along a length of the tube, although these are less common. These “pinhole” or larger failures may allow fluid to pass from a shell side to a tube side of an exchanger, or to pass from the tube side to a shell side of an exchanger, depending upon the size of the failure and the respective pressures of the fluids on each side.

Metallurgy of the heat exchanger may be designed for the fluids being passed through the exchanger. For example, a process fluid may contain a corrosive compound, and the metallurgy of the process side of the exchanger, as well as upstream and downstream equipment, may be designed to handle the corrosive compound. However, the heat exchange medium used to heat or cool (e.g., a refrigerant) the process fluid within the exchanger may be non-corrosive, and the metallurgy of the equipment (tanks, pumps, valves, etc.) associated with the heat exchange medium circulation system may not be designed to handle the corrosive compound. Initial design considerations for the overall system are typically based on the “typical” flow to be encountered, and expensive metallurgy for portions of the process not expected to encounter corrosive fluids is not used to save capital expense of the overall system. Due to the differences in design metallurgy, corrosive compounds leaked from a higher pressure process side of an exchanger to a lower pressure heat exchange medium side (e.g., refrigerant side) of an exchanger may result in contact of the corrosive compounds with metals not suited for such, and unwanted corrosion of equipment throughout the heat exchange medium circulation system may result.

Systems and processes herein are directed towards detecting leaks into a heat exchange medium circulation system, such as a refrigeration system, so that the undesirable corrosion of pipes, tanks, valves, pumps, and other equipment within the refrigeration system may be avoided or minimized. While described herein with respect to a refrigeration system, one skilled in the art may equally apply the teachings herein to systems circulating a hot heat exchange fluid used for heating of a process fluid.

Systems herein include a heat exchanger, having a process side and a refrigerant side. The process fluid flows on the process side of the exchanger, cooled by refrigerant flowing on the refrigerant side of the exchanger. The process fluid includes a corrosive compound, and the process side is configured to operate at a higher pressure than the refrigerant side. Due to the pressure difference, leaks may result in flow of the corrosive fluid from the higher pressure process side to the lower pressure refrigerant side.

The system also includes a refrigerant circulation system, which may be an open loop or a closed loop system. The refrigerant circulation system includes a refrigerant feed pipe fluidly connected to and configured to provide a flow of refrigerant to an inlet of the refrigerant side of the heat exchanger, as well as a refrigerant effluent pipe fluidly connect to and configured to receive a flow of refrigerant from an outlet of the refrigerant side of the exchanger.

The system further includes one or more sensors configured to measure a property of the refrigerant circulating in the refrigerant circulation system. For example, one or more temperature sensors may be disposed upstream and/or downstream of the heat exchanger. As another example, one or more flow rate sensors may be disposed upstream and/or downstream of the heat exchanger. As yet another example, one or more pressure sensors may be disposed upstream and/or downstream of the heat exchanger. Some embodiments may include combinations of these sensors upstream and/or downstream of the heat exchanger.

The system also includes a digital control system. The digital control system may receive a signal from the one or more sensors, such as a signal from a temperature sensor, a signal from a pressure sensor, or a signal from a flow rate sensor. The digital control system may be configured to convert the signals, which may be provided in volts or amps, for example, to a measured unit, such as ° C., kg/h, barg, or other units commonly used for temperature, volume or mass flow, or pressure, among other properties that may be measured, and to display the measurement to an operator via a display device, for example.

The digital control system of embodiments herein is configured to provide an alert, such as an audible or visual alarm, when a signal (measurement) from at least one of the one or more sensors is indicative of an active leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.

For example, the one or more sensors may include a temperature sensor configured to measure a temperature of the refrigerant in the refrigerant circulation system. The digital control system may be configured to provide an alert when a temperature indicated by the signal from the temperature sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. Introduction of hot process fluid into the refrigerant may result in a rise or a spike in the measured refrigerant temperature, indicating a leak has occurred.

As another example, the one or more sensors may include a pressure sensor configured to measure a pressure of the refrigerant in the refrigerant circulation system. The digital control system may be configured to provide an alert when a pressure indicated by the signal from the pressure sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. Introduction of the higher pressure process fluid into the lower pressure refrigerant may result in a rise or a spike in the measured refrigerant pressure, indicating a leak has occurred.

As yet another example, the one or more sensors may include a flow rate sensor configured to measure a flow rate of the refrigerant in the refrigerant circulation system. The digital control system may be configured to provide an alert when a flow rate indicated by the signal from the flow rate sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. Addition of process fluid to the refrigerant flow may result in an increase or spike in the measured flow rate of the refrigerant, indicating a leak has occurred.

Some embodiments may include combinations of these various sensors and associated alerts.

Continuous chemical processes generally operate at a “steady state,” other than during startup, shutdown, or transitions. During steady state operations, flows, temperatures and pressures will fluctuate to a minor degree. For example, steady state temperatures may include fluctuations in temperature by a few tenths of a degree to as much as a few degrees around a set point. Similarly, pressure and flow rates may fluctuate around a set point, the control systems being used to control valves, pumps, and other equipment in order to maintain the set points and steady operations. Often, the process side of the operations is of primary concern, as that is the side that controls product quality and throughput. Fluctuations on the utility or refrigerant side are of lesser concern, and fewer instrumentation and sensors are used; as long as the process side is operating properly, it is generally of less concern as to how much the refrigerant side fluctuates.

In contrast, embodiments herein utilize sensors on the refrigerant side to detect leaks of corrosive fluids, so as to be able to quickly act to avoid corrosion throughout the refrigeration system. Alarms or alerts may be provided where the temperature, pressure, or flow is indicative of a leak into the refrigerant system, the fluctuation in one or more of these values being greater than what is typical for steady state operations. The atypical values may be a percentage or a delta from the steady state set point, and may be 5%, 7.5%, 10%, above/below the steady state set point, or may be a few degrees, a few bar, or a few kg/h (or other flow measurement unit) above/below the steady state set point, which when occurring, may result in an audible or visual alarm provided by the control system. In other embodiments, the atypical value may be a delta value, such as a difference between inlet and outlet flow, inlet and outlet temperature, or inlet and outlet pressure. For example, a refrigerant may be provided to an inlet at a given pressure or temperature, with an expected pressure drop or temperature rise occurring across the exchanger, resulting in an outlet pressure or temperature. The (in-out) value may fluctuate over a typical range during “steady” operations; however, the difference between in and out and the typical delta may go outside the expected range when a leak occurs. In other words, alarms may be configured based on a single measured value according to some embodiments, or alarms may be configured based on a combination of measured values according to other embodiments. Operational alarms (investigative) may be provided in addition to the leak alarms (action required), and may be set at a lesser value or delta closer to the typical steady state range of operations.

The audible or visual alarms provided may indicate to an operator that a leak is occurring and that remedial action needs to be taken. For example, following the alert, the heat exchanger may be isolated, taken out of service, and inspected to find the leak(s). The leak(s) may then be fixed, such as by replacing tube sheets or tube bundles or the entire exchanger, or the leak may be bypassed, such as by plugging an inlet end of a leaking tube, among other possible actions that could prevent further flow of process fluid into the refrigerant side of the exchanger. Isolation of the heat exchanger may be performed manually by operators. In some embodiments, however, the digital control system may be configured to isolate the heat exchanger automatically when the signal is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. As it may be undesired to take an exchanger out of service, as this may impact upstream and downstream operations, parallel heat exchangers may be provided, and the digital control system may be configured to place a parallel heat exchanger in service while taking the leaking exchanger out of service, opening and closing respective valves so as to effect the transition of operations between the parallel heat exchangers. Where multiple parallel exchangers are provided and are used concurrently, the control system may be configured to take one or more of the leaking parallel exchangers out of service and to transition the process operations to reduced rates in view of the resulting reduced heat exchange capacity.

Embodiments herein thus provide for additional sensors, not typically used or considered during plant design and construction, so as to provide preventative measures during operation of the plant. Embodiments herein further provide for additional digital control system configurations to provide the alarms or alerts. The configuration of the sensors, controls, and control systems may be system dependent, and may depend on numerous factors, as may be appreciated by one skilled in the art. The additional capital expense of these sensors and controls is well valued, however, in view of the damage that may be avoided and the associated capital saved following a leak event.

A particular processing facility in which the above described systems for detecting leaks into a refrigeration system may be beneficial is a natural gas processing facility 46, as illustrated in FIGS. 2-4 , where like numerals represent like parts. Natural gas vapors 48 may be received from a crude processing plant 47, in which a crude oil feed is, for example, fed to a high pressure production trap (not illustrated), a low pressure production trap (not illustrated), a low pressure degassing tank (not illustrated), and a crude stabilizer (not illustrated), each of which may result in production of vapor streams 48 containing light hydrocarbons (methane, ethane, propane, butanes) and acid gases (such as H2S, CO2, and COS, among others) being provided to a feed gas header 49. These vapors 48 are fed to a compressor section 50 of the natural gas processing facility, which may include one or more feed drums 52, compressors 54, interstage coolers 56, knock out drums 58, and after coolers 60.

Following compression, a compressed raw natural gas stream 62, which may include both liquids and vapors, is produced and fed to a stripping and deethanizer section 70 of the natural gas processing facility. Stripping and deethanizing section 70 is configured to remove condensable components from the raw natural gas, such as propane and butanes, as these are more valuable components. The stripping section may include a feed surge drum 71, a stripper 72, and a deethanizer 74 to effect the desired separation of condensable and non-condensable components. Each of the stripper and deethanizer may be reboiled columns, each including a steam 75 driven reboiler 77, for example. Liquids 76, 78 recovered respectively as a bottoms from each column may then be combined as a natural gas liquids product 80.

Vapors from feed surge drum 71 and overheads 84 from stripper 72 may be fed to a TEG (tri ethylene glycol) system 88 for gas dehydration and dewpoint control. The dehydrated natural gas may then be fed to a propane chiller 94, a heat exchanger using propane as a refrigerant to reduce a temperature of the dehydrated natural gas. The chilled feed 95 may then be provided to deethanizer 74 for separation of ethane and lower boiling components, recovered as an overheads 90, from propane and higher boiling components recovered as bottoms 78. Overheads 90 is processed through a propane condenser 92, providing reflux 91 to the deethanizer. Non-condensed vapors 114 from the deethanizer overheads 90 are passed to an off gas compression section 99, which compresses the light vapors 100 to a desired pipeline pressure for feed to a downstream gas plant (not illustrated). A bypass 98 may be provided from the stripper 72 to the off gas compression section 99, which may be used in the event of a leak detection or other need to shut down or reduce the capacity of deethanizer 74.

FIG. 3 provides a closer view of the flows associated with the deethanizer 74 according to embodiments herein. Offgas (overheads) 101 from the stripper 72 are fed to the TEG system 88 for dehydration and dewpoint control. The dehydrated effluent 102 from the TEG system is then fed to propane chiller(s) 94, collected in a deethanizer feed drum 104, and fed to the deethanizer 74 via flow line 106. Deethanizer 74, as noted above, separates ethane and lower boiling components, recovered as an overheads 90, from propane and higher boiling components, recovered as a bottoms fraction 78, which may be recovered as a natural gas liquids product or fed to a downstream refinery (not illustrated).

Heat may be supplied to the deethanizer via a steam 75 driven reboiler 77. The overheads 90 may be passed through propane condenser(s) 92, a heat exchanger using propane as a refrigerant to at least partially condense the overhead vapors recovered from the deethanizer, providing reflux 91 to the deethanizer 74 and producing an off-gas 114, which, as noted above, is fed to an off gas compression section 99, which compresses the light vapors to a desired pipeline pressure for feed to a downstream gas plant (not illustrated).

The propane chiller 94 and the propane condenser 92 are each provided propane refrigerant 148 from a closed loop propane refrigerant system 150 as illustrated in FIG. 4 . As illustrated in FIG. 4 , each of the propane chiller and the propane condenser systems include two heat exchangers, operating in parallel. One may be in service while the other is on standby, or both may be operating at the same time.

To provide refrigeration to the propane chillers, liquid propane may be routed from a propane storage drum 152, reduced in pressure and temperature via a control valve 154, producing a vapor/liquid mixture, collected in a medium pressure flash drum 156. Liquid propane 157 may then be fed from the medium pressure flash drum 156 to the propane chillers 94. The liquids may be further reduced in temperature by flashing across valves 158. Heating of the propane in the propane chillers (cooling the dehydrated natural gas from the TEG system prior to feed to the deethanizer), results in propane vapors 160 that may then be compressed and cooled for continued use in the closed loop refrigeration system.

Similarly, to provide refrigeration to the propane condensers, liquid propane may be routed from propane storage drum 152, reduced in pressure and temperature via a control valve 170, producing a vapor/liquid mixture collected in a low pressure flash drum 172. Liquid propane 174 may then be fed from the low pressure flash drum 172 to the propane chillers 92. The liquid propane 174 may be further reduced in temperature by flashing across valves 176. Heating of the propane in the propane condensers (cooling and at least partially condensing the deethanizer overheads fed to the deethanizer reflux drum), results in propane vapors 180 that may then be compressed and cooled for continued use in the closed loop refrigeration system.

The collected warmed propane vapors from the condensers 92 and chillers 94 may be compressed via compressor(s) 186, cooled in a propane cooler 188, and fed to propane storage drum 152, completing the closed loop circuit. Various additional valves and knock-out drums are also illustrated in FIG. 4 , the function of which would be readily understood by one skilled in the art.

Incomplete removal of water in the TEG system, such as due to process upsets or otherwise, along with the presence of acid gases in the natural gas being processed, may result in acidic condensate forming in the low temperature propane chillers and propane condensers. This acidic condensate may result in corrosion within the propane chillers and propane condensers. This corrosion, in turn, may then result in leaks from the higher pressure natural gas side of the heat exchangers into the refrigeration side of the exchangers. Propane chillers have operating pressures, for example, of 360-365 psig on the natural gas (hydrocarbon) side and 70-80 psig on the refrigerant (propane) side of the exchanger. Propane condensers have, for example, operating pressures of 350-360 psig on the natural gas side and 35-45 psig on the refrigerant side of the exchanger. Such pressure differentials may provide for flow of acid-containing hydrocarbons into the refrigerant side of the exchanger and from there into the other components of the refrigerant circulation system (piping, knock out drums, compressor(s), flash drums, coolers, storage drums, etc.). As the metallurgy of the refrigeration loop may be carbon steel or other lower grade metals, as not designed for acid gas exposure, any leak of acidic components into the refrigerant loop may result in corrosion. In addition to the corrosion and leaks within the chillers and condensers, circulation of the acidic components through knock-out drums, the compressor, the propane cooler, and the propane storage drum may result in corrosion of one or more of these pieces of equipment. Valves, piping and other equipment associated with the refrigerant loop may also be damaged by the acidic components.

To prevent or minimize corrosion of the refrigerant loop due to process fluid leaks, embodiments of natural gas processing systems herein provide for leak detection. The natural gas processing facility, and more particularly the propane refrigerant loop, includes one or more sensors configured to measure a property of the propane refrigerant circulating in the closed loop refrigerant circulation system. For example, one or more temperature sensors may be disposed upstream and/or downstream of the propane chillers and propane condensers. As another example, one or more flow rate sensors may be disposed upstream and/or downstream of the propane chillers and propane condensers. As yet another example, one or more pressure sensors may be disposed upstream and/or downstream of the propane chillers and propane condensers. Some embodiments may include combinations of these sensors upstream and/or downstream of the propane chillers and propane condensers.

Where chillers and condensers are provided in parallel, temperature, pressure, and/or flow sensors may be provided on the propane supply line(s) and propane effluent line(s) from the exchangers. Where exchangers are both operating at the same time, it may be desirable to provide sensors associated with the individual supply and effluent lines associated with each exchanger, while sensors may be provided on common supply and effluent lines where the exchangers are arranged in parallel but not operated concurrently (operational plus backup configuration).

Referring still to FIG. 4 , the system also includes a digital control system 199 (control lines between various valves and the control system are not illustrated). The digital control system may receive a signal from the one or more sensors (not illustrated), such as a signal from a temperature sensor, a signal from a pressure sensor, a signal from a level sensor, or a signal from a flow rate sensor. The digital control system may be configured to convert the signals, which may be provided in volts or amps, for example, to a measured unit, such as ° C., kg/h, barg, or other units commonly used for temperature, volume or mass flow, level, or pressure, and to display the measurement to an operator via a display device, for example.

The digital control system of natural gas processing facilities according to embodiments herein is configured to provide an alert, such as an audible or visual alarm, when a signal (measurement) from at least one of the one or more sensors is indicative of an active leak from the process side (hydrocarbon side) of the heat exchanger to the refrigerant side (propane refrigerant side) of the propane chillers or propane condensers.

For example, the one or more sensors may include temperature sensors configured to measure temperatures of the refrigerant in the refrigerant circulation system, such as upstream and downstream of the chillers 94 and upstream and downstream of the condensers 92. Temperature sensors, for example, may be located at both upstream and downstream of the chillers and condensers, individually, or on common flow lines upstream and downstream of the respective exchangers. The digital control system may be configured to provide an alert when a temperature indicated by the signal from the temperature sensors is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. Introduction of hot process fluid into the refrigerant may result in a rise or a spike in the measured propane refrigerant effluent 160, 180 temperatures, indicating a leak has occurred. As the sour hydrocarbon is at a high temperature (130-150° F.) whereas the propane refrigerant is at a cold temperature (40-60° F.), should there be a leak in the propane heat exchanger tubes, a high temperature, as compared to typical “steady state” operational fluctuations in temperature, is observed in the propane circuit. Accordingly, a high priority temperature alarm is set for a temperature sensor appropriately located within the loop, such as downstream of an exchanger, to indicate the leak. As noted above, the alarm may be based on a delta between the exchanger inlet and outlet propane temperatures, or may be associated with an individual sensor.

As another example, the one or more sensors may include pressure sensor(s) configured to measure a pressure of the refrigerant in the refrigerant circulation system. Pressure sensors, for example, may be located at both upstream and downstream of the chillers and condensers, individually, or on common flow lines upstream and downstream of the respective parallel exchangers. The digital control system may be configured to provide an alert when a pressure indicated by the signal from one or more of the pressure sensors is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. Introduction of the higher pressure process fluid into the lower pressure refrigerant may result in a rise or a spike in the measured refrigerant pressure, indicating a leak has occurred. As there is a significant pressure difference between hydrocarbon and propane sides of the exchangers, pressure within the refrigerant loop, or a portion thereof, is used as a leak detection method, where a high pressure, as compared to typical “steady state” operational fluctuations in pressure, is indicative of a hydrocarbon leak through the heat exchangers into the propane loop. Accordingly, a high priority pressure alarm is set for a pressure sensor located in the loop to indicate the leak.

As yet another example, the one or more sensors may include a flow rate sensor configured to measure a flow rate of the refrigerant in the refrigerant circulation system. Flow rate sensors, for example, may be located at both upstream and downstream of the chillers and condensers, individually, or on common flow lines upstream and downstream of the respective parallel exchangers. The digital control system may be configured to provide an alert when a flow rate indicated by the signal from the flow rate sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. Addition of process fluid to the refrigerant flow may result in an increase or spike in the measured flow rate of the refrigerant, indicating a leak has occurred. As the propane refrigerant loop is a closed loop system, a leak of fluids into the closed loop may result in an increased overall flow within the loop or a portion thereof, as compared to typical “steady state” operational fluctuations in flow. Accordingly, a high priority flow rate alarm is set for a temperature sensor located in the loop to indicate the leak.

Similar to the flow rate concerns, introduction of the sour gas into the propane refrigerant loop via a leak may result in accumulation of excess fluids within the otherwise closed loop system. The excess fluids in the propane storage drum or other drums within the system may thus begin to accumulate, and levels within the refrigeration loop vessels may results in an increased level of liquids as compared to typical “steady state” operational fluctuations in level. Accordingly, a high priority alarm may be set for a level sensor located in the loop to indicate the leak. While a leak may be detected, and is desirably detected and remediated, much sooner via temperature, pressure and/or flow sensors on the propane refrigerant loop of natural gas processing systems herein, level sensor alarms may be useful as a backup, if desired, or may be used as a “check” to verify a leak has indeed occurred.

As yet another manner of detecting a leak, an increase in flow, pressure, or changes in other variables may impact a load on the propane compressor. The compressor may be steam driven or electric, and a sensor may be provided to measure a workload needed to achieve the desired compression. A fluctuation in load as compared to typical “steady state” operational fluctuations in load may be indicative of a leak, and a high load alarm may accordingly be set for the load sensor.

One or more of the above alarm triggers may be used to proactively detect and indicate a leak or a possible leak within the closed loop propane refrigerant system. In some embodiments, a combination of temperature, pressure, and flow sensors and alarms are used to detect a leak.

The audible or visual alarm may indicate to an operator that a leak is occurring, and that remedial action needs to be taken. For example, following the alarm, the heat exchanger in which the leak is occurring may be isolated, taken out of service, and inspected to find the leak(s). The leaks may then be fixed, such as by replacing tube sheets or tube bundles or the entire exchanger, or the leak may be bypassed, such as by plugging an inlet end of a leaking tube, among other possible actions that could prevent further flow of process fluid into the refrigerant side of the exchanger. Isolation of the heat exchanger may be performed manually by operators. In some embodiments, however, the digital control system may be configured to isolate the heat exchanger automatically when the signal is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger. As it may be undesired to rapidly take an exchanger out of service, as this may impact upstream and downstream operations, where parallel heat exchangers are provided, such as illustrated in FIG. 4 , the digital control system may be configured to place a parallel heat exchanger in service while taking the leaking exchanger out of service, opening and closing respective valves so as to effect the transition of operations between the parallel heat exchangers. Where both exchangers are operational during typical operations, and a leak is detected, the digital control system may be configured to take a leaking exchanger out of service while correspondingly reducing the process side flows to account for the reduced heat exchange capacity of the system, and/or bypassing a portion of the flow, such as from the stripper to the off gas compression via bypass 98, while the leak remediation efforts are undertaken.

As noted above, sensors may be provided for each exchanger. To effect the desired isolation of a leaking exchanger, isolation valves, controllable by the digital control system, may be provided upstream and downstream of each exchanger. Bleed valves, bleed piping, and other apparatus may be provided to enable the removal of fluids from a leaking exchanger so as to safely access and remediate the leak.

Large leaks or leaks not immediately detected and addressed may require a complete replacement (remove contaminated, provide fresh) of the propane within the refrigerant loop, such as via loop outlet 202 and make-up propane feed line 204. If the leak is isolated soon enough, only a partial bleed and replenishment may be necessary, such as from an isolated or isolatable portion of the refrigeration loop.

Methods and systems herein may include a digital control system configured to receive signals from one or more sensors. Digital control systems herein may also be configured to send signals to one or more valves, pumps, compressors, and other process equipment used to control operation of the various unit operations. Accordingly, implementations for operating the separation systems and refrigerant loops herein may be implemented on a computing system (e.g., a control system 199 as illustrated and described in FIG. 4 ) coupled to one or more controllers (associated with pumps, valves, compressors, etc.). The computing system may know a position or status of the controlled equipment, have finite control of the operations, and be able to have pumps speed up or slow down, valves open or close, etc.

Any combination of mobile, desktop, server, router, switch, embedded device, or other types of hardware may be used with the processes herein. For example, as shown in

FIG. 5 , the digital control system 199 may include one or more computer processors 802, non-persistent storage 804 (e.g., volatile memory, such as random access memory (RAM), cache memory), persistent storage 806 (e.g., a hard disk, an optical drive such as a compact disk (CD) drive or digital versatile disk (DVD) drive, a flash memory, etc.), a communication interface 812 (e.g., Bluetooth interface, infrared interface, network interface, optical interface, etc.), and numerous other elements and functionalities. It is further envisioned that software instructions in a form of computer readable program code to perform embodiments of the disclosure may be stored, in whole or in part, temporarily or permanently, on a non-transitory computer readable medium such as a CD, DVD, storage device, a diskette, a tape, flash memory, physical memory, or any other computer readable storage medium. For example, the software instructions may correspond to computer readable program code that, when executed by a processor(s), is configured to perform one or more embodiments of the disclosure, such as isolating a leaking exchanger or other operations noted above.

The control system 199 may also include one or more input devices 810, such as a touchscreen, keyboard, mouse, microphone, touchpad, electronic pen, or any other type of input device. The input devices may be used, for example, for setting or adjusting various operating parameters, as well as the operational alarm and leak alarm parameters. Additionally, the control system 199 may include one or more output devices 808, such as a screen (e.g., a liquid crystal display (LCD), a plasma display, touchscreen, cathode ray tube (CRT) monitor, projector, or other display device), a printer, external storage, or any other output device that may be used to display or alert a leak alarm, for example. One or more of the output devices may be the same or different from the input device(s). The input and output device(s) may be locally or remotely connected to the computer processor(s) 802, non-persistent storage 804, and persistent storage 806. Many different types of computing systems exist, and the aforementioned input and output device(s) may take other forms.

The control system 199 of FIG. 5 may include functionality to present raw and/or processed data, such as the aforementioned temperature sensor data, flow sensor data, or pressure sensor data, among others. For example, presenting data or alarm states may be accomplished through various presenting methods. Specifically, data or alarm states may be presented through a user interface provided by a computing device. The user interface may include a graphic user interface (GUI) that displays information on a display device, such as a computer monitor or a touchscreen on a handheld computer device. The GUI may include various GUI widgets that organize what data is shown as well as how data is presented to a user. Furthermore, the GUI may present data directly to the user, e.g., data presented as actual data values through text, or rendered by the computing device into a visual representation of the data, such as through visualizing a system model. For example, a GUI may first obtain a notification from a software application requesting that a particular data object be presented within the GUI. Next, the GUI may determine a data object type associated with the particular data object, e.g., by obtaining data from a data attribute within the data object that identifies the data object type. Then, the GUI may determine any rules designated for displaying that data object type, e.g., rules specified by a software framework for a data object class or according to any local parameters defined by the GUI for presenting that data object type. Finally, the GUI may obtain data values from the particular data object and render a visual representation of the data values within a display device according to the designated rules for that data object type.

Data or alarm states may also be presented through various audio methods. In particular, data may be rendered into an audio format and presented as sound through one or more speakers operably connected to a computing device. Data may also be presented to a user through haptic methods. For example, haptic methods may include vibrations or other physical signals generated by the computing system. For example, data may be presented to a user using a vibration generated by a handheld computer device with a predefined duration and intensity of the vibration to communicate the data.

As described above, embodiments of the present disclosure provide sensors, controls, control system configurations to detect a leak and isolate the leak from other portions of a refrigeration system. Embodiments herein advantageously provide for early leak detection and remediation, avoiding or minimizing damage to other portions of the refrigeration system, and thus avoiding or minimizing the expense and time that may be associated with corrective actions needed as a result of exposure of the refrigeration loop equipment to corrosive compounds. While such are typically not provided to minimize initial capital expenses associated with a facility, the present inventors have found that the additional sensors, controls, and control system configurations provided according to embodiments herein provide substantial long-term savings to a facility via the early detection and remediation of leaks. Embodiments herein additionally advantageously negate the need for expensive and complicated compositional measurement sensors and devices, while still providing the ability to rapidly detect a leak event.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function. 

What is claimed:
 1. A natural gas processing facility, comprising: a feed line providing a mixture of acid gases, methane, ethane, propane, and optionally butane and other heavier hydrocarbons; a compression section comprising one or more compressors configured to receive the mixture from the feed line, increase a pressure of the mixture and output a compressed mixture of methane, ethane, propane, and acid gases; a flow line for providing the compressed mixture to a stripper, the stripper configured to separate the compressed mixture into an overhead product comprising the acid gases, methane, ethane, and at least a portion of the propane and a bottoms product comprising propane and any butane and other heavier hydrocarbons; a propane chiller configured to receive the overhead product, chill the overhead product, and output a chilled overhead product; a flow line for providing the chilled overhead product to a deethanizer, the deethanizer configured to separate the chilled overhead product into an overhead fraction comprising the acid gases, methane and ethane, and a bottoms product comprising propane and any butane and other heavier hydrocarbons; an overhead condenser configured to condense at least a portion of the overhead fraction, provide reflux to the deethanizer, and to output an overhead vapor product comprising methane, ethane, and acid gases; a closed loop refrigeration system configured to provide a refrigerant to each of the propane chiller and the overhead condenser; one or more sensors configured to measure a property of the refrigerant, wherein the one or more sensors are disposed along a refrigerant feed line providing a refrigerant flow to the propane chiller or to the overhead condenser, along a refrigerant effluent flow line from the propane chiller or the overhead condenser, or both; a digital control system configured to: receive a signal from each of the one or more sensors; provide an alert when a signal from one of the one or more sensors is indicative of a leak of acid gases into the closed loop refrigeration loop.
 2. The system of claim 1, wherein the one or more sensors comprise a pressure sensor configured to measure a pressure of the refrigerant in the refrigerant system; a temperature sensor configured to measure a temperature of the refrigerant in the refrigerant system; and a flow rate sensor configured to measure a flow rate of the refrigerant flow in the refrigerant system.
 3. The system of claim 1, wherein the one or more sensors comprise: a feed temperature sensor disposed along a refrigerant feed line providing a refrigerant flow to the propane chiller, and an effluent temperature sensor along a refrigerant effluent flow line from the propane chiller, and wherein the digital control system is configured to provide an alert based upon a temperature of the effluent temperature sensor, a difference in temperature between the feed temperature sensor and the effluent temperature sensor, or both; and a condenser feed temperature sensor disposed along a refrigerant feed line providing a refrigerant flow to the overhead condenser, and an effluent temperature sensor along a refrigerant effluent flow line from the overhead condenser, and wherein the digital control system is configured to provide an alert based upon a temperature of the condenser effluent temperature sensor, a difference in temperature between the condenser feed temperature sensor and the condenser effluent temperature sensor, or both.
 4. The system of claim 1, wherein the one or more sensors comprise: a feed pressure sensor disposed along a refrigerant feed line providing a refrigerant flow to the propane chiller, and an effluent pressure sensor along a refrigerant effluent flow line from the propane chiller, and wherein the digital control system is configured to provide an alert based upon a pressure of the effluent pressure sensor, a difference in pressure between the feed pressure sensor and the effluent pressure sensor, or both; and a condenser pressure temperature sensor disposed along a refrigerant feed line providing a refrigerant flow to the overhead condenser, and a condenser effluent pressure sensor disposed along a refrigerant effluent flow line from the overhead condenser, and wherein the digital control system is configured to provide an alert based upon a pressure of the condenser effluent pressure sensor, a difference in pressure between the condenser feed pressure sensor and the condenser effluent pressure sensor, or both.
 5. The system of claim 1, wherein the one or more sensors comprise: a feed temperature sensor disposed along a refrigerant feed line providing a refrigerant flow to the propane chiller, and an effluent temperature sensor along a refrigerant effluent flow line from the propane chiller, and wherein the digital control system is configured to provide an alert based upon a temperature of the effluent temperature sensor, a difference in temperature between the feed temperature sensor and the effluent temperature sensor, or both; a condenser feed temperature sensor disposed along a refrigerant feed line providing a refrigerant flow to the overhead condenser, and an effluent temperature sensor along a refrigerant effluent flow line from the overhead condenser, and wherein the digital control system is configured to provide an alert based upon a temperature of the condenser effluent temperature sensor, a difference in temperature between the condenser feed temperature sensor and the condenser effluent temperature sensor, or both; a feed pressure sensor disposed along a refrigerant feed line providing a refrigerant flow to the propane chiller, and an effluent pressure sensor along a refrigerant effluent flow line from the propane chiller, and wherein the digital control system is configured to provide an alert based upon a pressure of the effluent pressure sensor, a difference in pressure between the feed pressure sensor and the effluent pressure sensor, or both; and a condenser pressure temperature sensor disposed along a refrigerant feed line providing a refrigerant flow to the overhead condenser, and a condenser effluent pressure sensor disposed along a refrigerant effluent flow line from the overhead condenser, and wherein the digital control system is configured to provide an alert based upon a pressure of the condenser effluent pressure sensor, a difference in pressure between the condenser feed pressure sensor and the condenser effluent pressure sensor, or both.
 6. The system of claim 1, wherein the closed loop refrigeration system comprises a compressor for compressing the refrigerant, wherein the one or more sensors comprise a sensor configured to measure a load on the turbine, and wherein the control system is configured to provide an alert when a turbine work load is indicative of leak.
 7. The system of claim 1, wherein the control system is configured to isolate the propane chiller when the one or more sensors are indicative of a leak in the propane chiller, and wherein the control system is configured to isolate the overhead condenser when the one or more sensors are indicative of a leak in the overhead condenser.
 8. A system for detecting leaks into a refrigeration system, the system comprising: a heat exchanger comprising a process side and a refrigerant side, the process side configured to operate at a higher pressure than the refrigerant side; a refrigerant circulation system including: a refrigerant feed pipe fluidly connected to and configured to provide a refrigerant to an inlet of the refrigerant side of the heat exchanger; a refrigerant effluent pipe fluidly connected to and configured to receive a refrigerant from an outlet of the refrigerant side of the heat exchanger; one or more sensors configured to measure a property of the refrigerant; a digital control system configured to provide an alert when a signal from at least one of the one or more sensors is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.
 9. The system of claim 8, wherein the digital control system is further configured to isolate the heat exchanger when the signal is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.
 10. The system of claim 8, wherein: the one or more sensors comprises a temperature sensor configured to measure a temperature of the refrigerant in the refrigerant circulation system; and the digital control system is configured to provide an alert when a temperature indicated by the signal from the temperature sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.
 11. The system of claim 8, wherein: the one or more sensors comprises a pressure sensor configured to measure a pressure of the refrigerant in the refrigerant circulation system; and the digital control system is configured to provide an alert when a pressure indicated by a signal from the pressure sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.
 12. The system of claim 8, wherein: the one or more sensors comprises a flow rate sensor configured to measure a flow rate of the refrigerant in the refrigerant circulation system; and the digital control system is configured to provide an alert when a flow rate indicated by a signal from the flow rate sensor is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.
 13. The system of claim 8, wherein the digital control system is configured to isolate the heat exchanger when a signal from at least one of the one or more sensors is indicative of a leak from the process side of the heat exchanger to the refrigerant side of the heat exchanger.
 14. A process for processing natural gas liquids, the process comprising: chilling a feed comprising acid gases, methane, ethane, and propane via indirect heat exchange with a refrigerant in a heat exchanger, wherein the feed is at a higher pressure than the refrigerant; measuring a temperature, pressure and/or flow of refrigerant feed and effluent to and from the heat exchanger, respectively; detecting a leak, automatically via a digital control system, based on a change or relative change in a measured temperature, pressure, or flow of refrigerant in the refrigerant loop upstream and/or downstream of the heat exchanger.
 15. The process of claim 14, further comprising isolating, automatically via the digital control system, the heat exchanger having the leak. 